As the consumer and commercial market for the distribution of data and video information expands, the industry is striving for design of high performance, secure, and inexpensive scrambling devices for preventing unauthorized users and providing adequate security performance. In the pay-per-view data and video distribution industry, where set-top boxes are installed at customer sites, it is extremely important to keep the costs down.
The previously implemented signal scrambling systems are mostly designed based on the encryption schemes. These techniques are generally considered to be expensive for the consumer market as the processing is performed in the digital domain, thus requiring high-speed analog-to-digital (A/D) and digital-to-analog (D/A) converters.
In using the analog-to-digital and digital-to-analog converters, there is often a trade-off between cost and performance. Higher resolution and higher speed of conversion are required for the signals where high fidelity is a crucial design guideline, such as a video signal containing moving objects. It may not always be possible to maximize the resolution and conversion speed while minimizing cost; thus a decision has to be made as to which are the most important requirements for a particular system. High conversion speeds are required for signals at video rates (7-20 MHz) which typically demand a trade-off between the resolution and cost.
The present invention provides a standalone CCD-based scrambling technique which operates on the signal in the analog domain, and provides performance comparable to, or better than, digital, but at lower cost. The CCD-based device can have additional on-chip functions performed, such as timing circuitry and the like. In particular, the device is suitable for scrambling of the analog video signal to render it unviewable but capable of high fidelity reconstruction and being displayed without any need for modification to standard video equipment.
CCD technology has been used for many years. CCD image sensing technology is widely developed for the commercial and military camera market. However, recent advances in CCD design and fabrication have led designers to consider new applications for this technology. For example, see Weinberg et al. U.S. Pat. No. 5,126,682, which relates to an inexpensive and highly integrated demodulation system incorporating CCD devices.
The CCD is a combination of analog and digital circuitry which benefits from the advantages of both worlds. Its analog input matches well with wideband and narrow-filtered signals and the device can produce a digital output when directly integrated with an A/D converter. Furthermore, the device may be controlled and clocked digitally thereby providing a natural interface with a system processor. When configured as an analog shift-register or delay line with temporary storage capability to support waveform scrambling in the analog domain, the CCD offers several key features including:
analog-domain processing without a need for A/D and D/A conversion
wideband input that readily accommodates video bandwidths
wide input dynamic range
variable clocking rates of KHz-to-at least 10's of MHz
independent input and output clocking rates (i.e., can provide rates buffering)
large number of stages
very low power consumption charge domain processing
direct and fast sample retrieval
The present invention provides a high level of security against unauthorized descrambling of the processed waveform. The waveform is shuffled in the analog domain in a random sequence which is known only to the descrambling device. This feature is particularly useful in the pay-per-view video distribution industry where a video title is downloaded to a pre-authorized customer via the existing cable TV or other transport links, scrambled by the set-top box and recorded on the VCR tape, all in realtime. The set-top box is used to de-scramble the VCR output for display on the TV screen at a later time. As both the scrambling and de-scrambling functions are integrated in the set-top design, the low cost of the analog, CCD-based scrambling technique is of significant importance.
Adequate security codes are included in the scrambled signal to assure that the tape can only be de-scrambled by the original scrambling set-top box. Timing and billing information can also be included to prevent the set-top box from de-scrambling after a preset deadline expires. The additional security, timing and billing information can be inserted either at the source distribution center or downloaded to the set-top.